This invention relates to the field of dynamic magnetic information storage and/or retrieval, and more specifically to a record transport with one or more rotating heads which record and/or reproduce machine-convertible information while moving, i.e., rotating, in transducing relationship with a magnetic web or tape, this information being oriented as magnetic domains to form information tracks which extend generally transverse to the longitudinal tape length.
More specifically, this invention relates to transducing magnetic tape with a rotating magnetic head or transducer wherein a gas bearing is provided to support the tape in a stable manner along the path of a flying head. The stability of the gas bearing adjacent the rotating head is more critical for a flying head than it is for a head which moves in contact with the tape. Any fluttering of the tape due to an unstable gas bearing makes it difficult to control the flying height or separation between a rotating flying head and the magnetic tape.
As used herein, the term "gas bearing" is intended to encompass the use of a compressible fluid, such as air, to support the tape, and to the use of hydrodynamic and/or hydrostatic force in such a gas bearing. As used in the art, the term "hydrostatic" is equivalent to the term "externally-pressurized," and the term "hydrodynamic" is equivalent to the term "self-generated,"
Rotating head magnetic tape units are widely known. In one form of prior art device, a tape guiding structure in the form of a generally cylindrical mandrel or drum includes a rotating headwheel which carries one or more read/write heads. The magnetic tape engages the mandrel at one point, makes a helical wrap about at least a portion of the mandrel, and exits the mandrel at a point which is both axially and circumferentially spaced from the entrance point. The angle of helical tape wrap can vary in accordance with design choice, but is usually between 180.degree. and 360.degree.. The headwheel rotates so as to sweep its magnetic head or heads transversely across the tape. The angle at which the head enters and exits the tape may vary, in accordance with design choice, from slightly less than 90.degree. to a small angle, such as 15.degree..
Another form of prior art device is one wherein the headwheel is associated with a tape guiding structure which bends the tape transversely into an arcuate shape that conforms to the circumferential shape of the headwheel. In this device the tape travels in a generally straight line past the headwheel, and is transversely bent by the associated guides as it enters the headwheel area.
The present invention finds utility with either aforementioned type of device, and has been found particularly useful with the helical wrap device.
A major problem encountered in the aforementioned devices is that of head/tape wear. Many known devices tolerate high wear conditions in favor of good transducing operation by causing the head to traverse the tape in contact therewith.
In order to reduce wear, numerous solutions have been proposed to provide lubrication as tape passes the rotating head.
For example, it has been proposed that one or both of the mandrel halves rotate to generate an air film. It has also been proposed that one of the mandrel halves rotate in a direction opposite to that of tape motion, and that this rotating mandrel carry a head which protrudes from the periphery, to contact the tape. The rotating mandrel half creates a self-acting or hydrodynamic air bearing. The protruding head mechanically lifts the tape, allowing air to be sucked under the portion of the tape which overlies the stationary mandrel half.
Yet another arrangement suggests that the rotating mandrel half be other than cylindrical, and specifically comprise a cylindrical portion and a frustro-conical portion.
Still other arrangements suggest that the two mandrel halves be rotated in opposite directions.
In yet another arrangement, the mandrel comprises a solid tube which rotates at a high speed in a direction opposite to that of the tape. The mandrel carries a head whose gap extends outwardly beyond the mandrel surface. The thickness of the air layer between the head gap and the tape is reduced by vacuum force, or by an air foil positioned adjacent the head gap. This air foil operates to increase the air velocity therearound, creating a low pressure area which, in turn, results in a reduction in the air pressure between the head gap and the tape.
Another generally different class of rotating head device provides two stationary, but spaced, mandrel halves, with a rotating headwheel located therebetween. In one of these arrangements, each of the mandrel halves includes a thin annular flange, adjacent the headwheel, which flanges extend a distance radially beyond the adjacent mandrel half. These flanges contact the tape and operate to produce localized tensioning in the tape in the vicinity of the head. A head is mounted on the headwheel, and the head physically contacts the tape.
In another arrangement of this type, the peripheral surface of the headwheel is substantially flush, but somewhat recessed, from the adjacent cylindrical surfaces of the two stationary mandrel halves. The rotation of the headwheel causes air to be entrained between the tape and the mandrel halves.
In yet another arrangement, a means is provided for lubricating the engagement of the tape and the rotor heads wherein a generally tapered headwheel carries a number of heads which protrude radially beyond the circumference of the headwheel. The tape/head lubrication is supplied by a volatile lubricant flow or spray which is applied a distance sufficiently far from the tape/head interface so that a portion of the lubricant volatilizes before reaching this interface.
The general concept of providing a stable flying head which is air-bearing separated from adjacent magnetic recording media is of course well known. In one arrangement, a flexible disk rotates relative to a stationary base plate to create a primary air bearing. A stationary head protrudes through this primary air bearing into the rotational plane of the disk. This head penetration creates a secondary air bearing between the head surface and the disk, which secondary air bearing affects a narrow separation between the head and the disk.
The present invention is directed to an improved rotating head device which provides good transducing operation while at the same time reducing head/tape wear by causing the head to fly out of contact with the adjacent tape inteface. The critical features of the present invention are the provision of three different levels of tape tension, these three tape tension levels establishing a stable gas bearing platform to support the tape adjacent the head's transducing gap.
As used herein, the term "flying" or "flying head" is intended to encompass a structure wherein the nominal head-to-tape spacing is in the range of a few microinches, for example, 5 to 20 microinches, and wherein the majority of the force exerted by the head on the tape is a pneumatic force. Occasional contact force, due to the head physically contacting raised portions of the generally rough tape recording surface, is not, however, precluded.
In its more specific aspects, the present invention contemplates a rotating head device wherein two spaced and stationary mandrels of the same diameter or cross-section cooperate with an intermediate headwheel of a larger diameter. This headwheel is preferably crowned or arc-shaped in cross-section, with the major diameter of the arc, measured at its apex, being larger than the adjacent mandrel diameters, and with the minor diameter of the arc, measured adjacent the mandrel, being less than the adjacent mandrel diameters. In this manner, the tape is locally stressed in a track overlying the headwheel. The headwheel carries a magnetic recording head which is mounted on the headwheel's major diameter and radially extends therebeyond. The surface of the head is such as to cause the head to fly in microinch adjacency to the tape's magnetic recording surface. The protruding head causes the tape to be locally stressed in a moving tent which overlies the head.
Thus, three significantly different levels of increasing tape stress are provided; namely, in the tape area adjacent the mandrel, in the tape track adjacent the headwheel, and in the moving tape tent adjacent the moving head.
As used herein, the term "arc-shaped" is intended to generically encompass any cross-section which is curved at the rotor edges adjacent the mandrel sections so as to support the adjacent tape on a thin gas bearing. In a preferred embodiment the rotor's edges are recessed below the adjacent surface of the mandrel.
As used herein, the term "head" is intended to encompass one or more magnetic transducing gaps.